Power limiter configuration for audio signals

ABSTRACT

Example embodiments provide a process that includes one or more of receiving an audio signal at a feedback compressor circuit, multiplying the received audio signal with a power feedback signal to create a product audio signal, wherein the feedback signal comprises a low-pass filtered signal, applying a power amplifier to the product audio signal, and providing the amplified product audio signal as an output signal to a speaker.

BACKGROUND OF THE INVENTION

A power limiter circuit configuration may utilize a feedback compressorarchitecture. Within such a configuration, an output amplitude ismonitored and compared against a threshold in the log domain. When theoutput amplitude exceeds the threshold, the difference, in decibels, ismeasured and multiplied by a constant loop gain to determine anattenuation amount. That attenuation is converted to a linear scalefactor, is low-pass filtered, and applied to the input signal. The timeconstant of the low-pass filter determines how quickly signalcompression is applied and released.

One reason for a feedback compressor, rather than a feedforwardcompressor, is that the relationship between amplitude and output poweris complex. The load impedance will vary with frequency, so the powerdissipation, based on voltage, will vary with frequency as well. Anattempt to predict output power by modelling the load could beperformed, but that would be computationally expensive and incurlatency. A feedback compressor permits the measurement of the trueoutput power from voltage and current measurements without needing todetermine the load.

Sensing circuits measure output voltage and current, and the results areconverted to digital using audio A/D converters. The digital values ofvoltage and current are multiplied to calculate power for the feedbackpath.

Amplifier output power is specified based on being able to output asinewave burst output waveform without attenuating or distorting thesignal. The burst signal waveform alternates repeatedly between ratedRMS output power for a short duration of time (typically 20-25 ms) andlow power for a much longer duration (typically hundreds ofmilliseconds). Because more time is spent at the lower power level, theoverall average power is much less than the burst rating. For example, a1200 W burst may only average 300 W of continuous output. Power limitingshould permit a 1200 W burst in order to call the product a 1200 Wamplifier.

For a simple compressor used for a 300 W limit and receiving a 1200 Wburst, the burst waveform will fail to pass unattenuated even if theaverage power of the burst over time is less than 300 W. That is becauseattenuation starts to be applied as soon as the output is over 300 W forany point in time.

SUMMARY OF THE INVENTION

The present application relates to a method that includes one or more ofreceiving an audio signal at a feedback compressor circuit, determininghow much to attenuate the audio signal when a power level of the audiosignal exceeds a threshold power level, combining the audio signal withan auxiliary attenuation signal from an auxiliary attenuation source anda compressed attenuation signal from the feedback compressor circuit tocreate a combination signal, and generating an audio output signal ofthe feedback compressor circuit based on the combination signal.

Another example embodiment may include an apparatus that includes areceiver configured to receive an audio signal at a feedback compressorcircuit, and a processor configured to determine how much to attenuatethe audio signal when a power level of the audio signal exceeds athreshold power level, combine the audio signal with an auxiliaryattenuation signal from an auxiliary attenuation source and a compressedattenuation signal from the feedback compressor circuit to create acombination signal, and generate an audio output signal of the feedbackcompressor circuit based on the combination signal.

Still yet another example embodiment may include a gate array configuredto store instructions that when executed cause a processor to performreceiving an audio signal at a feedback compressor circuit, determininghow much to attenuate the audio signal when a power level of the audiosignal exceeds a threshold power level, combining the audio signal withan auxiliary attenuation signal from an auxiliary attenuation source anda compressed attenuation signal from the feedback compressor circuit tocreate a combination signal, and generating an audio output signal ofthe feedback compressor circuit based on the combination signal.

Still yet a further example embodiment may include a non-transitorycomputer readable storage medium configured to store instructions thatwhen executed cause a processor to perform one or more of receiving anaudio signal at a feedback compressor circuit, receiving an auxiliaryattenuation signal from an auxiliary attenuation source, determining athreshold power level based on a value of the auxiliary attenuationsignal, determining an output power level of the audio signal exceedsthe threshold power level, combining the audio signal with the auxiliaryattenuation signal from the auxiliary attenuation source and acompressed attenuation signal from the feedback compressor circuit tocreate a combination signal, and generating an audio output signal ofthe feedback compressor circuit based on the combination signal.

Still yet a further example embodiment may include an apparatus thatincludes a receiver configured to receive an audio signal at a feedbackcompressor circuit, receive an auxiliary attenuation signal from anauxiliary attenuation source, and a processor configured to determine athreshold power level based on a value of the auxiliary attenuationsignal, determine an output power level of the audio signal exceeds thethreshold power level, combine the audio signal with the auxiliaryattenuation signal from the auxiliary attenuation source and acompressed attenuation signal from the feedback compressor circuit tocreate a combination signal, and generate an audio output signal of thefeedback compressor circuit based on the combination signal.

Still yet another example embodiment may include a non-transitorycomputer readable storage medium configured to store instructions thatwhen executed cause a processor to perform one or more of receiving anaudio signal at a feedback compressor circuit, receiving an auxiliaryattenuation signal from an auxiliary attenuation source, determining athreshold power level based on a value of the auxiliary attenuationsignal, determining an output power level of the audio signal exceedsthe threshold power level, combining the audio signal with the auxiliaryattenuation signal from the auxiliary attenuation source and acompressed attenuation signal from the feedback compressor circuit tocreate a combination signal, and generating an audio output signal ofthe feedback compressor circuit based on the combination signal.

Another example embodiment may include a method that includes receivingan audio signal from a feedback path of a feedback compressor circuit,determining whether an auxiliary attenuation value applied to thefeedback compressor circuit has changed since a last audio signal wasreceived, responsive to determining the auxiliary value has changed,determining a current operational state value of the LPF needs to bemodified based on the changed auxiliary attenuation value, modifying theoperational state value of the LPF, and applying the audio signal to themodified LPF.

Still another example embodiment may include an apparatus that includesa receiver configured to receive an audio signal from a feedback path ofa feedback compressor circuit, and a processor configured to determinewhether an auxiliary attenuation value applied to the feedbackcompressor circuit has changed since a last audio signal was received,responsive to the determination that the auxiliary value has changed,determine a current operational state value of the LPF needs to bemodified based on the changed auxiliary attenuation value, modify theoperational state value of the LPF, and apply the audio signal to themodified LPF.

Still yet another example embodiment may include a non-transitorycomputer readable storage medium configured to store instructions thatwhen executed cause a processor to perform one or more of receiving anaudio signal from a feedback path of a feedback compressor circuit,determining whether an auxiliary attenuation value applied to thefeedback compressor circuit has changed since a last audio signal wasreceived, responsive to determining the auxiliary value has changed,determining a current operational state value of the LPF needs to bemodified based on the changed auxiliary attenuation value, modifying theoperational state value of the LPF, and applying the audio signal to themodified LPF.

Yet another example embodiment may include a method that includes one ormore of receiving an audio signal at a feedback compressor circuit,multiplying the received audio signal with a power feedback signal tocreate a product audio signal, wherein the feedback signal comprises alow-pass filtered signal, applying a power amplifier to the productaudio signal, and providing the amplified product audio signal as anoutput signal to a speaker.

Still another example embodiment may include an apparatus that includesa receiver configured to receive an audio signal at a feedbackcompressor circuit, a processor configured to multiply the receivedaudio signal with a power feedback signal to create a product audiosignal, and the feedback signal includes a low-pass filtered signal,apply a power amplifier to the product audio signal, and provide theamplified product audio signal as an output signal to a speaker.

Still yet another further example may include a non-transitory computerreadable storage medium configured to store instructions that whenexecuted cause a processor to perform one or more of receiving an audiosignal at a feedback compressor circuit, multiplying the received audiosignal with a power feedback signal to create a product audio signal,wherein the feedback signal comprises a low-pass filtered signal,applying a power amplifier to the product audio signal, and providingthe amplified product audio signal as an output signal to a speaker.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of a feedback compressor circuit forburst power waveforms according to example embodiments.

FIG. 2 illustrates a block diagram of a feedback compressor circuit forburst power waveforms with auxiliary attenuation being added to thecompressor attenuation according to example embodiments.

FIG. 3 illustrates a block diagram of a feedback compressor circuit forburst power waveforms with a state update logic module used to manageauxiliary attenuation value and operation of a low-pass filter accordingto example embodiments.

FIG. 4 illustrates a block diagram of a feedback compressor circuit forburst power waveforms with a detailed example of the state update logicmodule according to example embodiments.

FIG. 5 illustrates a block diagram of a feedback compressor circuit forburst power waveforms with switch actuation and energy storage accordingto example embodiments.

FIG. 6 illustrates a block diagram of a feedback compressor circuit withan applied amplifier power, according to example embodiments.

FIG. 7A illustrates an example method of operation of a feedbackcompressor and applied auxiliary attenuation according to exampleembodiments.

FIG. 7B illustrates an example method of operation of a feedbackcompressor, updated logic and auxiliary attenuation according to exampleembodiments.

FIG. 7C illustrates an example method of operation of a feedbackcompressor, updated logic and LPF history for scaling and attenuationstrategies, according to example embodiments.

FIG. 7D illustrates an example method of operation of a feedbackcompressor with a power amplifier applied according to exampleembodiments.

FIG. 8 illustrates an example computing entity configured to storeinstructions and executed operations associated with example embodimentsof the application.

DETAILED DESCRIPTION

Example embodiments include circuit configurations illustrated aslogical systems and modules which perform certain tasks and operationsto process data, such as an audio input signal and provide a modifiedoutput signal. Such configurations may support additional and/or fastattenuation sources, and enabled and disabled compression for a storedenergy approach.

A load impedance will vary with frequency, and thus the powerdissipation based on voltage will also vary with frequency. A feedbackcompressor permits measuring a true output power from voltage andcurrent measurements without requiring information about the load.

FIG. 1 illustrates a block diagram of a feedback compressor circuit forburst power waveforms according to example embodiments. Referring toFIG. 1 , the configuration or ‘circuit’ 100 may include an audio input102, such as audio data from an audio source, which is multiplied by anexternal data source, such as sensors 110 which measure attenuationcaused by any one or more of a temperature sensor 112, a current sensor114 and/or a voltage sensor 116. The combination of one or more of thosesensor sources may be combined into an auxiliary attenuation source 104combined at multiplier 106. The result is multiplied, via multiplier108, with feedback from the compressor circuit which includes an audiopower measurement signal that has been filtered via a LPF 122, convertedto a logarithmic scale 124 and which is compared to a threshold 126 todetermine whether the output power is exceeding the threshold 126 tocreate a burst preserving feedback (BPF) loop.

Having the low-pass filter to the beginning of the circuit feedbackchain provides that attenuation will not be applied immediately inresponse to output power changes. Because the low-pass filter smoothsthe power measurement to calculate an average, the filter output lagsthe actual output power. The lag permits a passed burst test, since thefilter will not charge up to the limiter threshold during short bursts.By placing the low-pass filter in the front of the feedback chain, burstpower waveforms are preserved by the amplifier compressor circuit.

In the configuration of FIG. 1 , the audio input signal is multipliedtwice, once by the auxiliary attenuation 104 via multiplier 106 and onceby the compressor attenuation 115 (i.e., multiplier 109). The output maybe converted back to the linear domain via antilog conversion module128. A loop gain 118 of the feedback loop is applied to the filteredaudio signal. Loop gain is a standard part of a feedback compressorcircuit for controlling the compression ratio, which is the severity ofthe attenuation applied. For example, a compressor with a ratio of 10:1will attenuate a signal 10 dB over the threshold down to a level of 1 dBover the threshold. Increasing the loop gain increases the compressionratio. For purposes of this disclosure, it may be assumed the loop gainis a constant value which can be changed to achieve a higher compressionratio. One approach is to convert the auxiliary attenuation value intothe log domain and add it to the compressor attenuation directly sincemultiplication in the linear domain is equivalent to addition in the logdomain. Both FIGS. 1 and 2 are functionally equivalent since they bothrepresent two gain values (i.e., compressor attenuation 115 andauxiliary attenuation 104) being applied to the audio input signal toproduce the audio output signal 130. The audio output signal 130 may bethe same as the input signal 102 or may be an attenuated version of theinput signal. As long as the amplifier average output power is below aconfigurable threshold value then the output signal will be a copy ofthe input signal. When the amplifier average output power exceeds theconfigurable threshold then the output signal will be an attenuatedversion of the input signal that reduces the average output power to theconfigurable threshold. The output signal 130 will also be an attenuatedversion of the input signal if the auxiliary attenuation 104 is greaterthan zero. In one example, 6 dB of auxiliary attenuation indicates thatthe output will be the input signal 102 multiplied by 0.5.

FIG. 2 illustrates a block diagram of a feedback compressor circuit forburst power waveforms with auxiliary attenuation being added to thecompressor attenuation according to example embodiments. Referring toFIG. 2 , the configuration 200 provides a similar configuration to FIG.1 , however, the adder 111 adds the auxiliary attenuation 104 directlyto the compressor attenuation 115. This alternative produces a sameoutput audio signal 130. The “hold-off” time where no compression isapplied is directly related to the filter time constant. Long burstsignals cannot pass through without making the filter time constantlong, and detection of faults cannot be made quickly without making thefilter time constant short.

The filter is the digital equivalent of a simple resistor/capacitor (RC)low-pass filter (LPF). The filter is an exponential average with a fixedtime constant. For example purposes, embodiments may be using a simpleform of exponential smoothing. In this example, the filter time constantwas tuned empirically so that the overall design would not attenuate aburst test waveform but would protect from high power exceeding about100 ms. The filter time constant may be adjusted if needed. Also, thefilter time constant may be dynamically varied to optimize audiodistortion performance.

FIG. 3 illustrates a block diagram of a feedback compressor circuit forburst power waveforms with a state update logic module used to manageauxiliary attenuation value and operation of a low-pass filter accordingto example embodiments. Referring to FIG. 3 , the configuration 300introduces a state update logic module 140 which provides a controlfeature to control the operation of the LPF 122. Also, the thresholdcomparison operation 126 has a dynamic feature to adjust the thresholdbased on the auxiliary attenuation 104. For example, the thresholdcomparison 126 identifies an input signal and a threshold. The output isthe amount that the input exceeds the threshold. In one example, If(input>threshold), then output=input−threshold; or else the output=0.

In one example, to guarantee that 3 dB of auxiliary attenuation isapplied on top of existing compression attenuation, and does not causethe compressor to release, the threshold is adjusted by the auxiliaryattenuation amount. If the compressor loop circuit is activelycompressing and the value of auxiliary attenuation changes, thecompressor loop may overcorrect. This is because auxiliary attenuationchanges the threshold instantaneously, and the threshold is beingcompared with the slow-moving output of the low-pass filter. Forexample, if the compressor control loop has a time constant (Tc) of 100ms, and the compressor loop is applying 3 dB of attenuation (compressorattenuation), and the auxiliary attenuation increases by 1 dB, then thenext threshold comparison will have a result 1 dB greater than theprevious sample. The 1 dB change is multiplied by the loop gain andturns into a 20 dB change. The 20 dB change is applied until the 100 mscontrol loop catches up with the change in applied power. The actualattenuation will settle to the desired attenuation level eventually, butthere are massive overcorrections due to the threshold changing. Slowingdown the auxiliary attenuation changes is not an option since there arecases where the auxiliary attenuation must be applied quickly. Forexample, a response to clipping may be needed within 15 ms, which is toofast for the control loop to compensate. As a result, changes must bedetected in the auxiliary attenuation, and then applied to the state ofthe low-pass filter (LPF) 122 in the control loop. If the auxiliaryattenuation changes by 1 dB, the filter state must be changed by 1 dB aswell. This keeps the filter state synchronized with the auxiliaryattenuation so that the threshold comparison output does not jump inresponse to an auxiliary attenuation change.

With regard to threshold changes, prior to auxiliary attenuationchanges, the threshold itself is specifically the maximum average outputpower that is desired to be permitted. The negative feedback loop formedby the compressor will keep the actual average output power at or belowthat particular limit. For example, if 100 W continuous output power isdesired, the threshold may be configured based on 100 W. Since thecompressor expression operates in the log domain, 100 W is convertedinto the log domain as: 10*log 10(100 W)=20.0. So, the 100 W thresholdprior to auxiliary attenuation is 20.0. The auxiliary attenuation is avalue in decibels, such as 3.0 dB. Decibels are already a log domainunit, so they do not need any conversion. Since the auxiliaryattenuation and the threshold are both in the log domain, calculatingthe new threshold adjusted for auxiliary attenuation is a simplesubtraction: Thresholdnew=Threshold−AuxAttenuation;Thresholdnew=20.0−3.0; Thresholdnew=17.0.

FIG. 4 illustrates a block diagram of a feedback compressor circuit forburst power waveforms with a detailed example of the state update logicmodule according to example embodiments. Referring to FIG. 4 , theconfiguration 400 provides additional details regarding the operation ofthe state update logic 140. In an effort to control operation of the LPF122, history data 123 may be referenced and used to control the LPFvalues applied in the feedback loop.

The approach to modifying the LPF 122 does not require scaling thefilter output. Instead, the approach is to adjust the ‘state’ keptinside the filter history 123, such as in a memory coupled to thefilter. Each change to auxiliary attenuation is applied as a change tothe filter state, which permits a bypass to the slower control loop byapplying gain changes instantly without affecting the control loop. Inoperation, this approach is like temporarily speeding-up the controlloop to incorporate auxiliary attenuation immediately withoutinterfering with the long-term, slower compression attenuation producedby the control loop. The filter state is modified whenever the value ofthe auxiliary attenuation changes. This modifies the filter history sothe LPF can adjust to the detected changes immediately without a timelag.

The directly-adjustable time constant (Tc) is the Tc of the LPF. Becausethe LPF is in the feedback loop of the compressor, the LPF Tc directlyrelates to how quickly or slowly the audio level is adjusted. For thatreason, the filter time constant may also be referred to as thecompressor time constant.

It is common for compressor circuits in general to use a more complexfilter with two time constants to separate ramping up and ramping down,but the example embodiment generally have a single time constant. Usingseparate up/down time constants may result in a design that failed burstsignal tests.

The “filter state” is a digital signal processing term for values thatneed to be stored between calls to a difference equation. In this case,the difference equation result is stored because it is used in the nextiteration of the difference equation. Pseudocode for a differenceequation may provide: filter_state=0; // Initialize state. For eachinput: output=a*input−(1−a)*filter_state; filter_state=output. Changingthe filter state provides modifying the value of filter_state in thepseudocode. Pseudocode modifying the value of filter_state by 10×provides: filter_state=filter_state*10. That operation would be insertedbetween iterations of the loop. It only occurs when there is a change inthe auxiliary attenuation value. The filter state is scaled according tothe negative of the derivative of the auxiliary attenuation. Forexample, if the auxiliary attenuation changes from 1 dB to 4 dB, that isa change of +3 dB. We would apply that as a −3 dB change to thefilter_state. Note that filter_state is a linear power measurement, so−3 dB must be converted to the linear domain as: 10{circumflex over( )}(− 3/10)=0.5 (approximately). Thus: filter_state=filter_state*0.5.The approach of modifying the filter state could be applicable to morecomplex filters than the one currently used.

The value of the differentiator 144 “z−1” represents a delay of onesample of audio. The antilog conversion 142 permits the sample to beapplied directly to the LPF 122. The state update logic 140 uses thederivative of the auxiliary attenuation signal, produced by thedifferentiator 144, to determine how much the auxiliary attenuationvalue has changed since a previous sample. That change is converted to alinear scale factor and is used to scale the history (i.e., state)information 123 stored in the low-pass filter 122. If the auxiliaryattenuation signal 104 is not changing over a period of time, thederivative is ‘0’, which converts to a linear scale factor of ‘1’. Inthat case, the filter history has not changed since it is multiplied by‘1’.

FIG. 5 illustrates a block diagram of a feedback compressor circuit forburst power waveforms with switch actuation and energy storage accordingto example embodiments. Referring to FIG. 5 , in an alternative approachto having the LPF at the front of the feedback chain process in anattempt to pass burst tests, another approach 500 is to utilize acompression circuit switch (on/off) so that the switch is ‘on’ whenneeded and ‘off’ when not needed depending on the energy level appliedto the audio input signal. A way of determining when the compressionfeedback circuit is needed to amplify a signal is to identify when anaudio channel is low on energy. Conceptually, this circuit may beconsidered as having a ‘tank’ of available energy, such as aconfiguration of bulk capacitors on a main supply source.

Referring to FIG. 5 , the circuit may include additional features, suchas an amplifier 152, analog to digital converters (A/Ds) 155 and 157, acurrent sensor 154, and feedback current 156 and feedback voltage 158.The multiplier 121 combines the signals sent to the energy tank 162,which can be switched on to the feedback loop of the compressor circuitvia switch 166/167 under certain circumstances, for example, the “energytank” 162 may represent amplifier energy in real time. For each audiosample over time, there are two operations to update the tank energystate. For example, by incrementing the energy state based on powerprovided into the amplifier 152 from a power source (not shown), and bydecrementing an energy state based on the instantaneous output powermeasurement.

When the tank energy state drops below a minimum allowed energy tankenergy threshold (T_(E)), this triggers the compressor circuit to beenabled ‘on’. The compressor would be disabled after the tank rechargesto a maximum allowed tank energy level (T_(EMAX)). This permits the timeconstant (T_(c)) to be separated from the time that it takes thecompressor to start attenuating. The energy tank values determines whenthe compressor starts attenuating, and the low-pass filter valuesdetermines the time constant.

FIG. 6 illustrates a block diagram of a feedback compressor circuit withan applied amplifier power, according to example embodiments. Referringto FIG. 6 , the configuration provides an example where the currentfeedback 156 and the voltage feedback 158 are multiplied via multiplier121 to create a power feedback path 162 which is provided to the LPF122. This provides a way to limit the amount of output power of theaudio output signal 130. If the amount of power is too high then thethreshold comparison module 126 may cause the signal to be modifieddepending on whether the power level exceeds the threshold.

FIG. 7A illustrates an example method of operation of a feedbackcompressor and applied auxiliary attenuation according to exampleembodiments. Referring to FIG. 7A, the process 700 may include receivingan audio signal at a feedback compressor circuit 712, determiningwhether to attenuate the audio signal when a power level of the audiosignal exceeds a threshold power level 714, combining the audio signalwith an auxiliary attenuation signal from an auxiliary attenuationsource and a compressed attenuation signal from the feedback compressorcircuit to create a combination signal 716, and generating an audiooutput signal of the feedback compressor circuit based on thecombination signal 718.

The auxiliary attenuation signal may include a composite of attenuationsignals received from a plurality of sensors. The composite ofattenuation signals may include one or more of an excessive heat signal,an excessive output current signal and a power supply voltage sagsignal. The combining of the audio signal with the auxiliary attenuationsignal provides one or more of multiplying the audio signal by theauxiliary attenuation signal, and converting the auxiliary attenuationsignal to the log domain and adding the auxiliary attenuation signal tothe compressed attenuation signal. The process also includes filteringthe audio output signal via a low pass filter (LPF), providing afeedback signal to the LPF prior to combining the auxiliary attenuationsignal and the compressed attenuation signal, and the feedback signal isused to combine the audio signal with the auxiliary attenuation signaland the compressed attenuation signal to create the combination signal,and wherein the combination signal is combined with the audio signal tocreate the audio output signal.

FIG. 7B illustrates an example method of operation of a feedbackcompressor, updated logic and auxiliary attenuation according to exampleembodiments. Referring to FIG. 7B, the process 720 may include receivingan audio signal at a feedback compressor circuit 722, receiving anauxiliary attenuation signal from an auxiliary attenuation source 724,determining a threshold power level based on a value of the auxiliaryattenuation signal 726, determining an output power level of the audiosignal exceeds the threshold power level 728, combining the audio signalwith the auxiliary attenuation signal from the auxiliary attenuationsource and a compressed attenuation signal from the feedback compressorcircuit to create a combination signal 732, and generating an audiooutput signal of the feedback compressor circuit based on thecombination signal 734.

The process may also include dynamically adjusting a value of a low passfilter (LPF) based on a change to the threshold power level, andfiltering the audio output signal via the low pass filter (LPF),dynamically adjusting a value of a low pass filter (LPF) based on achange to the threshold power level, and filtering the audio outputsignal via the low pass filter (LPF). The process may also includecombining the filtered audio signal with the auxiliary attenuationsignal from the auxiliary attenuation source and the compressedattenuation signal from the feedback compressor circuit to create thecombination signal, and combining the combination signal with the audiosignal to create the audio output signal. The process may furtherinclude performing a logarithmic conversion to the filtered audio signalprior to combining the filtered audio signal with the auxiliaryattenuation signal, and performing an antilogarithmic conversion to thecombination signal prior to combining the combination signal with theaudio signal. The auxiliary attenuation signal may include a compositeof attenuation signals received from a plurality of sensors configuredto generate one or more of an excessive heat signal, an excessive outputcurrent signal and a power supply voltage sag signal.

FIG. 7C illustrates an example method of operation of a feedbackcompressor, updated logic and LPF history for scaling and attenuationstrategies, according to example embodiments. Referring to FIG. 7C, theprocess 740 may include receiving an audio signal from a feedback pathof a feedback compressor circuit 742, determining whether an auxiliaryattenuation value applied to the feedback compressor circuit has changedsince a last audio signal was received 744, responsive to determiningthe auxiliary value has changed, determining a current operational statevalue of the LPF needs to be modified based on the changed auxiliaryattenuation value 746, modifying the operational state value of the LPF748, and applying the audio signal to the modified LPF 752.

The process may also include determining the auxiliary attenuation valuehas changed, and responsive to determining the auxiliary attenuationvalue has changed, changing the operational state value of the LPF by avalue that is directly proportional to the change in the auxiliaryattenuation value, storing a plurality of operational state values ofthe LPF in a memory, and determining a derivative of the auxiliaryattenuation value as a basis to modify the operational state value ofthe LPF. The process may also include delaying the audio signal by oneaudio sample prior to applying the audio signal to the LPF, anddetermining an anti-log conversion of the audio signal prior to applyingthe audio signal to the LPF, dynamically adjusting the operational statevalue of the LPF based on a change to a threshold power level, andfiltering the audio output signal via the low pass filter (LPF). Also,the auxiliary attenuation signal may include a composite of attenuationsignals received from a plurality of sensors configured to generate oneor more of an excessive heat signal, an excessive output current signaland a power supply voltage sag signal.

FIG. 7D illustrates an example method of operation of a feedbackcompressor with a power amplifier applied according to exampleembodiments. Referring to FIG. 7D, the process 760 may include receivingan audio signal at a feedback compressor circuit 762, multiplying thereceived audio signal with a power feedback signal to create a productaudio signal, wherein the feedback signal comprises a low-pass filteredsignal 764, applying a power amplifier to the product audio signal 766,and providing the amplified product audio signal as an output signal toa speaker 768.

The process may also include multiplying a current feedback signal and avoltage feedback signal of the amplified product audio signal to createa power feedback signal, providing the power feedback signal to alow-pass filter to create the low-pass filtered signal, performing athreshold comparison of the low-pass filtered signal to a thresholdvalue to determine whether an output signal power level is exceedingthreshold value, and when the output signal power is exceeding thethreshold value, subtracting the threshold value from the input signallevel. The process may also include performing a logarithmic conversionof the low-pass filtered signal prior to performing the thresholdcomparison, and performing an antilogarithmic conversion to the powerfeedback signal prior to multiplying the power feedback signal with thereceived audio signal.

Another example process may include receiving an audio signal at afeedback compressor circuit, determining whether a power supply level ofan energy source of the feedback compressor circuit has dropped below apower level threshold, determining whether to enable or disable a switchto activate the feedback compressor circuit based on whether the powersupply level has dropped below the power level threshold, and applyingpower to the audio signal via the energy source. When the power supplylevel of the energy source has dropped below the power level threshold,the process provides for enabling the switch to activate the feedbackcompressor circuit, and when the power supply level of the energy sourcehas increased beyond an energy source level threshold, enabling theswitch to deactivate the feedback compressor circuit. In anotherexample, the energy source of the feedback compressor circuit is adisposed in the feedback compressor circuit and includes a plurality ofcapacitors. The method may also include determining, via operation ofthe energy source, when the feedback compressor circuit experiencesattenuation, and determining, via operation of a low pass filter (LPF)of the feedback compressor circuit, a compression time constant.

FIG. 8 illustrates an example computing entity configured to storeinstructions and executed operations associated with example embodimentsof the application, such as an example network entity device configuredto store instructions, software, and corresponding hardware forexecuting the same, according to example embodiments of the presentapplication.

The operations of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in acomputer program executed by a processor, or in a combination of thetwo. A computer program may be embodied on a computer readable medium,such as a storage medium. For example, a computer program may reside inrandom access memory (“RAM”), flash memory, read-only memory (“ROM”),erasable programmable read-only memory (“EPROM”), electrically erasableprogrammable read-only memory (“EEPROM”), registers, hard disk, aremovable disk, a compact disk read-only memory (“CD-ROM”), or any otherform of storage medium known in the art.

FIG. 8 is not intended to suggest any limitation as to the scope of useor functionality of embodiments of the application described herein.Regardless, the computing node 800 is capable of being implementedand/or performing any of the functionality set forth hereinabove.

In computing node 800 there is a computer system/server 802, which isoperational with numerous other general purpose or special purposecomputing system environments or configurations. Examples of well-knowncomputing systems, environments, and/or configurations that may besuitable for use with computer system/server 802 include, but are notlimited to, personal computer systems, server computer systems, thinclients, rich clients, hand-held or laptop devices, multiprocessorsystems, microprocessor-based systems, set top boxes, programmableconsumer electronics, network PCs, minicomputer systems, mainframecomputer systems, and distributed cloud computing environments thatinclude any of the above systems or devices, and the like.

Computer system/server 802 may be described in the general context ofcomputer system-executable instructions, such as program modules, beingexecuted by a computer system. Generally, program modules may includeroutines, programs, objects, components, logic, data structures, and soon that perform particular tasks or implement particular abstract datatypes. Computer system/server 802 may be practiced in distributed cloudcomputing environments where tasks are performed by remote processingdevices that are linked through a communications network. In adistributed cloud computing environment, program modules may be locatedin both local and remote computer system storage media including memorystorage devices.

As shown in FIG. 8 , computer system/server 802 in cloud computing node800 is shown in the form of a general-purpose computing device. Thecomponents of computer system/server 802 may include, but are notlimited to, one or more processors or processing units 804, a systemmemory 806, and a bus that couples various system components includingsystem memory 806 to processor 804.

The bus represents one or more of any of several types of busstructures, including a memory bus or memory controller, a peripheralbus, an accelerated graphics port, and a processor or local bus usingany of a variety of bus architectures. By way of example, and notlimitation, such architectures include Industry Standard Architecture(ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA)bus, Video Electronics Standards Association (VESA) local bus, andPeripheral Component Interconnects (PCI) bus.

Computer system/server 802 typically includes a variety of computersystem readable media. Such media may be any available media that isaccessible by computer system/server 802, and it includes both volatileand non-volatile media, removable and non-removable media. System memory806, in one embodiment, implements the flow diagrams of the otherfigures. The system memory 806 can include computer system readablemedia in the form of volatile memory, such as random-access memory (RAM)810 and/or cache memory 812. Computer system/server 802 may furtherinclude other removable/non-removable, volatile/non-volatile computersystem storage media. By way of example only, storage system 814 can beprovided for reading from and writing to a non-removable, non-volatilemagnetic media (not shown and typically called a “hard drive”). Althoughnot shown, a magnetic disk drive for reading from and writing to aremovable, non-volatile magnetic disk (e.g., a “floppy disk”), and anoptical disk drive for reading from or writing to a removable,non-volatile optical disk such as a CD-ROM, DVD-ROM or other opticalmedia can be provided. In such instances, each can be connected to thebus by one or more data media interfaces. As will be further depictedand described below, memory 806 may include at least one program producthaving a set (e.g., at least one) of program modules that are configuredto carry out the functions of various embodiments of the application.

Program/utility 816, having a set (at least one) of program modules 818,may be stored in memory 806 by way of example, and not limitation, aswell as an operating system, one or more application programs, otherprogram modules, and program data. Each of the operating system, one ormore application programs, other program modules, and program data orsome combination thereof, may include an implementation of a networkingenvironment. Program modules 818 generally carry out the functionsand/or methodologies of various embodiments of the application asdescribed herein.

As will be appreciated by one skilled in the art, aspects of the presentapplication may be embodied as a system, method, or computer programproduct. Accordingly, aspects of the present application may take theform of an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present application may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Computer system/server 802 may also communicate with one or moreexternal devices 820 such as a keyboard, a pointing device, a display822, etc.; one or more devices that enable a user to interact withcomputer system/server 802; and/or any devices (e.g., network card,modem, etc.) that enable computer system/server 802 to communicate withone or more other computing devices. Such communication can occur viaI/O interfaces 824. Still yet, computer system/server 802 cancommunicate with one or more networks such as a local area network(LAN), a general wide area network (WAN), and/or a public network (e.g.,the Internet) via network adapter 826. As depicted, network adapter 826communicates with the other components of computer system/server 802 viaa bus. It should be understood that although not shown, other hardwareand/or software components could be used in conjunction with computersystem/server 802. Examples include, but are not limited to: microcode,device drivers, redundant processing units, external disk drive arrays,RAID systems, tape drives, and data archival storage systems, etc.

Although an exemplary embodiment of at least one of a system, method,and non-transitory computer readable medium has been illustrated in theaccompanied drawings and described in the foregoing detaileddescription, it will be understood that the application is not limitedto the embodiments disclosed, but is capable of numerous rearrangements,modifications, and substitutions as set forth and defined by thefollowing claims. For example, the capabilities of the system of thevarious figures can be performed by one or more of the modules orcomponents described herein or in a distributed architecture and mayinclude a transmitter, receiver or pair of both. For example, all orpart of the functionality performed by the individual modules, may beperformed by one or more of these modules. Further, the functionalitydescribed herein may be performed at various times and in relation tovarious events, internal or external to the modules or components. Also,the information sent between various modules can be sent between themodules via at least one of: a data network, the Internet, a voicenetwork, an Internet Protocol network, a wireless device, a wired deviceand/or via plurality of protocols. Also, the messages sent or receivedby any of the modules may be sent or received directly and/or via one ormore of the other modules.

One skilled in the art will appreciate that a “system” could be embodiedas a personal computer, a server, a console, a personal digitalassistant (PDA), a cell phone, a tablet computing device, a smartphoneor any other suitable computing device, or combination of devices.Presenting the above-described functions as being performed by a“system” is not intended to limit the scope of the present applicationin any way but is intended to provide one example of many embodiments.Indeed, methods, systems and apparatuses disclosed herein may beimplemented in localized and distributed forms consistent with computingtechnology.

It should be noted that some of the system features described in thisspecification have been presented as modules, in order to moreparticularly emphasize their implementation independence. For example, amodule may be implemented as a hardware circuit comprising custom verylarge-scale integration (VLSI) circuits or gate arrays, off-the-shelfsemiconductors such as logic chips, transistors, or other discretecomponents. A module may also be implemented in programmable hardwaredevices such as field programmable gate arrays, programmable arraylogic, programmable logic devices, graphics processing units, or thelike.

A module may also be at least partially implemented in software forexecution by various types of processors. An identified unit ofexecutable code may, for instance, comprise one or more physical orlogical blocks of computer instructions that may, for instance, beorganized as an object, procedure, or function. Nevertheless, theexecutables of an identified module need not be physically locatedtogether but may comprise disparate instructions stored in differentlocations which, when joined logically together, comprise the module andachieve the stated purpose for the module. Further, modules may bestored on a computer-readable medium, which may be, for instance, a harddisk drive, flash device, random access memory (RAM), tape, or any othersuch medium used to store data.

Indeed, a module of executable code could be a single instruction, ormany instructions, and may even be distributed over several differentcode segments, among different programs, and across several memorydevices. Similarly, operational data may be identified and illustratedherein within modules and may be embodied in any suitable form andorganized within any suitable type of data structure. The operationaldata may be collected as a single data set or may be distributed overdifferent locations including over different storage devices, and mayexist, at least partially, merely as electronic signals on a system ornetwork.

It will be readily understood that the components of the application, asgenerally described and illustrated in the figures herein, may bearranged and designed in a wide variety of different configurations.Thus, the detailed description of the embodiments is not intended tolimit the scope of the application as claimed but is merelyrepresentative of selected embodiments of the application.

One having ordinary skill in the art will readily understand that theabove may be practiced with steps in a different order, and/or withhardware elements in configurations that are different than those whichare disclosed. Therefore, although the application has been describedbased upon these preferred embodiments, it would be apparent to those ofskill in the art that certain modifications, variations, and alternativeconstructions would be apparent.

While preferred embodiments of the present application have beendescribed, it is to be understood that the embodiments described areillustrative only and the scope of the application is to be definedsolely by the appended claims when considered with a full range ofequivalents and modifications (e.g., protocols, hardware devices,software platforms etc.) thereto.

What is claimed is:
 1. A method comprising: multiplying an audio signalwith a power feedback signal to create a product audio signal, whereinthe feedback signal comprises a low-pass filtered signal; performing athreshold comparison of the low-pass filtered signal to a thresholdvalue to determine whether an output signal power is exceeding thethreshold value, wherein when the output signal power is exceeding thethreshold value, subtracting the threshold value from the audio signal;and amplifying the product audio signal as an output signal to aspeaker.
 2. The method of claim 1, comprising: multiplying a currentfeedback signal and a voltage feedback signal of the amplified productaudio signal to create the power feedback signal.
 3. The method of claim2, comprising: providing the power feedback signal to a low-pass filterto create the low-pass filtered signal.
 4. The method of claim 1,comprising: receiving the audio signal at a feedback compressor circuit.5. The method of claim 1, comprising: performing a logarithmicconversion of the low-pass filtered signal.
 6. The method of claim 5,wherein the logarithmic conversion is performed prior to performing thethreshold comparison.
 7. The method of claim 3, comprising: performingan antilogarithmic conversion to the power feedback signal prior tomultiplying the power feedback signal with the audio signal.
 8. Anapparatus comprising: a processor configured to multiply an audio signalwith a power feedback signal to create a product audio signal, whereinthe feedback signal comprises a low-pass filtered signal; perform athreshold comparison of the low-pass filtered signal to a thresholdvalue to determine whether an output signal power is exceeding thresholdvalue, wherein when the output signal power is exceeding the thresholdvalue, subtract the threshold value from the audio signal; and amplifythe product audio signal as an output signal to a speaker.
 9. Theapparatus of claim 8, wherein the processor is further configured tomultiply a current feedback signal and a voltage feedback signal of theamplified product audio signal to create the power feedback signal. 10.The apparatus of claim 9, wherein the processor is further configured toprovide the power feedback signal to a low-pass filter to create thelow-pass filtered signal.
 11. The apparatus of claim 8, comprising areceiver configured to receive the audio signal at a feedback compressorcircuit.
 12. The apparatus of claim 8, wherein the processor is furtherconfigured to perform a logarithmic conversion of the low-pass filteredsignal.
 13. The apparatus of claim 12, wherein the logarithmicconversion is performed prior to performing the threshold comparison.14. The apparatus of claim 10, wherein the processor is furtherconfigured to perform an antilogarithmic conversion to the powerfeedback signal prior to the power feedback signal being multiplied withthe audio signal.
 15. A non-transitory computer readable storage mediumconfigured to store instructions that when executed cause a processor toperform: multiplying an audio signal with a power feedback signal tocreate a product audio signal, wherein the feedback signal comprises alow-pass filtered signal; performing a threshold comparison of thelow-pass filtered signal to a threshold value to determine whether anoutput signal power is exceeding the threshold value, wherein when theoutput signal power is exceeding the threshold value, subtracting thethreshold value from the audio signal; and amplifying the product audiosignal as an output signal to a speaker.
 16. The non-transitory computerreadable storage medium of claim 15, wherein the processor is furtherconfigured to perform: multiplying a current feedback signal and avoltage feedback signal of the amplified product audio signal to createthe power feedback signal.
 17. The non-transitory computer readablestorage medium of claim 15, wherein the processor is further configuredto perform: providing the power feedback signal to a low-pass filter tocreate the low-pass filtered signal.
 18. The non-transitory computerreadable storage medium of claim 15, wherein the processor is furtherconfigured to perform: receiving the audio signal at a feedbackcompressor circuit.
 19. The non-transitory computer readable storagemedium of claim 15, wherein the processor is further configured toperform: performing a logarithmic conversion of the low-pass filteredsignal.
 20. The non-transitory computer readable storage medium of claim19, wherein the logarithmic conversion is performed prior to performingthe threshold comparison.